August 2012

[This will be brief and sloppy, since I should be packing, not blogging. With luck, there will be an update later this month/year/decade, but don’t hold your breath.]

Today went like this:

5:00 a.m. Wake up a good four hours before my usual wakey-uppy time, because in order to get to the Marvin Hamlisch Memorial Choir rehearsal, I had to catch the 6:21 train.

7:45 a.m. – 1:00 p.m. Rehearse for and sing at Marvin’s funeral. While it isn’t the subject of this post, highlights of the event were a) President Bill Clinton, b) John Updike’s Perfection Wasted, a sucker punch if there ever was one, and c) Terre Blair Hamlisch’s heartbreakingly stunning eulogy to her late husband.

12:45 – 2:30 p.m. Lunch at Serafina on 61st (a martini and a plate of paglia e fieno) with fellow singers Andy, Darcy, and the just-married Baninos. Disappointingly, although we were all dressed in black, no one asked “Who died?” Only in New York.

Here’s the hard-boiled truth. The latest research on eggs and heart disease is flawed. Eggs are not going to kill you.

Jezebel and othernewsoutlets have jumped on Eggyolk consumption and carotid plaque, a paper recently published in the journal Atherosclerosis, which claims that a person’s carotid plaque increases exponentially with their egg yolk consumption. (This paper is referred to below as EWKY, for Eggs Will Kill You.)

Most likely there is no exponential relationship at all. But if you believe the authors’ statistics, perhaps you will believe what I can prove by an identical analysis:

The length of objects, measured in centimeters, grows exponentially with length measured in inches.

Of course, this is ridiculous. The length of an object in centimeters is exactly 2.54 times its length in inches. The relationship is linear, not exponential. After you finish reading this post, I hope you’ll realize that the egg slander in Atherosclerosis is also ridiculous.

The “exponential” dependence of plaque on egg yolk consumption is an artifact of skewed data.

I created a data set with the same distribution as the EWKY data to investigate a hypothetical relationship between inches and centimeters, using the same flawed way the authors of EWKY analyzed the relationship between egg yolk consumption and plaque.

Briefly, the authors of EWKY treated “quintile” as a scale variable, which it is not.

Here are the histograms of my data and the EWKY data. Pretty much the same.

And here are error bar charts of my data and the EWKY data. Both appear to show a clearly non-linear relationship.

The error bar chart from EWKY is the sole justification for the claim of an exponential cigarette-like relationship to plaque:

(My error bars are much shorter because the correlation between inches and centimeters is perfect. While the relationship between egg-yolk years and plaque is not, it’s nevertheless not exponential.)

There are other statistical gaffes in EWKY, but I don’t have time to delve into them. I’ll mention the worst very quickly.

First, most of the EWKY analysis compares lifetime egg yolk consumption to plaque. Lifetime anything consumption is a proxy for age, and atherosclerosis is strongly age-dependent. Nowhere do the authors of EWKY provide convincing evidence that the relationship between egg yolk consumption and plaque is anything but an artifact of the proxy for age.

Furthermore, the authors pay no heed to the always-important question of effect size. They provide a single analysis that shows a statistically significant relationship between the non-age-proxy measurement of egg yolk consumption per week (as opposed to over a lifetime) and plaque that’s independent of age:

The difference in plaque area between the <2 eggs/week group and the 3 or more eggs group (an arbitrary split, and ignoring the several hundred subjects who ate from 2 to 2.99 eggs/week) is about 1/20 of a standard deviation, otherwise known as squat. The fact that p < 0.0001 after adjustment for age is irrelevant, because with such a large sample, significance might appear for an even smaller effect (micro-squat).